The present invention broadly relates to weaving machines, and more specifically concerns itself with a new and improved apparatus for controlling the insertion of the weft thread in a weaving machine, especially, although not exclusively, a weaving machine working with air jet operated insertion means for the weft thread.
In a prior art weaving machine as known, for example, from German Patent Publication No. 3,002,862 published July 30, 1981, and the cognate copending U.S. application Ser. No. 226,542 filed Jan. 21, 1981, now U.S. Pat. No. 4,458,726 a sensor is arranged on the catch side of the weaving shed and senses the moment of time when the front end of the weft-thread arrives. In response thereto the weft insertion velocity at the related weft insertion mechanism is automatically increased or decreased by a control means depending upon whether the moment of time of arrival of the weft thread is too late or too early relative to a corresponding position of the main shaft of the weaving machine. In this arrangement there is also taken into account in conjunction with the weft insertion velocity the adjustment of the moment of time braking of the inserted weft thread by a weft-thread brake arranged on the weft insertion side of the weaving shed. Consequently, the moment of time of braking of the weft thread is shifted to an earlier moment of time simultaneously with the readjustment of the weft insertion velocity to a higher value, and conversely to a later moment of time simultaneously with the readjustment of the weft insertion velocity to a lower value.
Such arrangement has the disadvantage that the weft-thread ends which protrude from the weaving shed on the catch side thereof can have different lengths. When each of the weft-thread ends are cut-off at the weaving machine, there possibly arises a relatively large loss of weft-thread material. When the weft-thread ends, for example, are inwardly turned to form a weaving selvedge, such selvedge may possess a relatively large width in the presence of increased lengths of the weft-thread ends. It is possible for the width of the weaving selvedge to vary, for example, when the weft thread is infed or inserted by means of an air jet and the length of the infed weft threads is not always exactly the same.